Introduction to RACH Procedure in 5G

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This video explains how a UE establishes its initial connection using RACH procedure in 5G.

▬ Contents of this video ▬▬▬▬▬▬▬▬▬▬

0:00 - Introduction
0:39 -SSB Burst
2:21 - RACH Transmission (Message 1)
2:41 - Zadoff Chu Sequences
5:05 - Timing Advance Command (Message 2)
5:26 - RRC Connection Request (Message 3)
5:40 - Contention Resolution (Message 4)
7:53 - Contention Free RACH procedure

Correction: 6:18 - UE sends *ue-identiy* in "RR Connection Request" (Msg3), not TC-RNTI. *ue-identiy* is typically a random number, hence it will be different for UE 1 and UE 2. Base Station selects one of the *ue-identity* and sends it over "Contention Resolution" (Msg4). UE matches received *ue-identity* with its own *ue-identity* to check if its RACH attempt is a Success or Failure.

References:
1. ETSI TS 138 211
2. ETSI TS 138 321
3. Textbook “5G New Radio in Bullets” by Chris Johnson

Music: Erik SATIE - Gymnopedies 1

#5G, #RACH, #Wireless, #WirelessCommunication, #CellularCommunication
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Highly impressed with the content and the presentation. Looking forward to see more videos

chaitugable
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Very clear video with minimum time wastage. Loved it

amitsardanayt
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Appreciate your presentation. The topic is neatly explained in a simplest way. I saw very few videos. Could you please cover more topics. Thanks

kirankumaryakkala
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Thanks for such a brief video. Can you also make a separate video based on Zadoff Chu sequence, that would be incredibly helpful.

ayushibhatt
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Thanks for the video, it was very clear!
I have a question, does this mean there is a miniscule chance of two UEs ending up with the same C-RNTI, if the selected ue-identity is also the same?

thepromisedlan
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TC-RNTI is issued by gNB to UE in MSG2 first, not MSG4. The UE uses the TC-RNTI to scramble the uplink PUSCH message (MSG3).

shan
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Excellent. It would be great to do the same for 4G.
Thank you

JEANCLAUDEJOSEPHBADJI
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@02:30, it says, UE sends the message after time offset?! What exactly is time offset?

gunjangosain
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When and where does RA-RNTI comes into picture???

sukshithshetty
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First Question, how will one UE know which Zad Off Chu seq was selected by other UE??

sukshithshetty